Lighting control over specific areas is desirable so that areas not occupied can have their lights extinguished, thereby conserving substantial electrical energy. Motion detectors such as microwave detectors, passive infrared detectors, ultrasonic detectors, and other active or passive devices can be used for both burglar alarm detection and light control systems. When the building is not occupied, a motion detector is used for security or entry detection. When the building is occupied, the same sensor can be used to control the lighting.
When used to control lighting, the motion detector should be sensitive to initial motion without producing false alarms, which would unnecessarily turn on the room lights. However, if the motion detector is adjusted to minimize false entry alarms, motion associated with a subsequent low-activity task such as reading, may not be detected and the lights would then be extinguished. Utilizing a higher detector sensitivity (or lower detection threshold) would permit detection of the continued presence, but would make the lighting control system vulnerable to false alarms during the unoccupied time, which will cause the lights to come on, reducing the power savings to be produced by the light control system. Therefore a motion detector having a fixed sensitivity for all applications will either have an excessive number of false alarms for a room-unoccupied condition, or a limitation in the inability to detect a continued presence within the room.